The present invention relates generally to power transmission chains. The invention has particular application to power transmission chains of the roller chain variety, which are used in engine timing applications as well as industrial applications.
Power transmission chains are widely used in the automotive industry. Such chains are used for engine timing drives as well as for the transfer of power in a transfer case. Power transmission chains are also widely used in. industrial applications.
One type of chain is known as xe2x80x9croller chainxe2x80x9d. A typical roller chain consists of alternate inner links and outer links. The inner links, which are also known as xe2x80x9cbushingxe2x80x9d links, consist of spaced link plates with bushings tightly received in openings, or apertures, at each end of the links. The outer links, which are also known as xe2x80x9cpinxe2x80x9d links, consist of spaced links plates with pins tightly received in openings, or apertures, at each end of the sidebars. The bushings freely rotate about the pins to pivotally connect the outer links to the inner links in alternate arrangement. Rollers are provided on the bushings, and when the roller chain is wrapped about a sprocket, the teeth of the sprocket are received between the laterally spaced sidebars and the longitudinally spaced rollers. An example of roller chain is found in U.S. Pat. No. 4,186,617, which is incorporated herein by reference.
Roller chains can include both xe2x80x9ctrue rollerxe2x80x9d and rollerless design. The true roller design includes the described rollers mounted about the bushings. Rollerless chain contains bushings that directly contact the sprocket. Both types of roller chain are typically specified in industry as British Standard chain and American National Standards Institute (ANSI) chain.
A conventional roller chain drive is comprised of a roller chain wrapped about at least two sprockets supported by shafts. The chain is endless and assembled from interconnected links that are adapted to fit over and about teeth formed on the sprockets. Movement of a driving sprocket causes power transmission through the chain and consequent movement of a driven sprocket. In an engine timing drive application, the driving sprocket may be mounted on the engine crankshaft and the driven sprocket mounted on a valve camshaft. The rotation of the camshaft is thus controlled by the rotation of the crankshaft through the roller chain. Timing drive applications can include the use of a power transmission chain to drive a plurality of sprockets or in the camshaft to camshaft drive in an overhead camshaft engine.
Noise is associated with chain drives. Noise is generated by a variety of sources, but in roller chain drives it can be caused by the impact sound generated by the collision of the chain and the sprocket at the onset of meshing. The loudness of the impact sound is affected, by among other things, the impact velocity between the chain and the sprocket and the impact of the steel rollers or bushings against the steel or powdered metal sprockets.
Many efforts have been made to decrease the noise level and pitch frequency distribution in chain drives of both the silent chain and the roller chain variety. Modification of sound patterns in silent chain drives was addressed in U.S. Pat. No. 4,342,560, by changing the configuration of link flanks. In U.S. Pat. Nos. 3,377,875 and 3,495,468, the sprocket teeth were relieved to achieve noise reduction in contacts between the silent chain and sprocket. Other efforts to reduce noise resulted in use of phased chain and sprocket systems as shown in U.S. Pat. No. 5,397,280.
A problem with conventional roller chains is directed to the bushings. The bushings of conventional roller chains are typically cylinders formed from flat metal. Formation of the bushing leaves a longitudinal seam along one edge. During assembly of the roller chain, the seam, if located at a point of contact with the pin may cause rapid wear in the chain and may cause premature lengthening or failure of the chain.
Another major problem associated with chains of conventional construction is that the strength and elasticity of the inner links and the outer links may vary significantly. Attempts to address this issue via special guide link designs are exemplified by Avramidis, U.S. Pat. No. 4,915,675, and Bremer, U.S. Pat. No. 2,602,344. Whereas these methods have resulted in measurable improvements, results are better when these methods are applied in transmission chains in which the conventional links are stronger. With the weaker and less rigid links of timing chains and, particularly, the links of narrow timing chains, the results are less successful because the strength discrepancy between the sprocket engaging inner links and the guide links is substantial.
In addition, in chains of conventional construction, because there are at least two different types of links, problems often arise associated with variance of lengths of the different links.
The present invention includes a chain which is constructed of fewer types of parts than a conventional roller chain. The present invention seeks to provide a modified roller chain wherein the pins directly engage the sprocket teeth for power transmission. The present invention seeks to provide several embodiments for noise reduction. The present invention also seeks to provide a simplified chain construction that is stronger in a given width, has improved wear characteristics and is more simple and economical to manufacture than a conventional roller chain.
In accordance with one embodiment of this invention, a modified roller chain is provided which avoids the use of conventional bushings and rollers. Instead, a central pin directly contacts the sprocket teeth. The modified roller chain, provided for use with a pair or a series of sprockets, includes a series of interleaved inner links and outer links. The inner and outer links are made up of the same type of link plate. Each link plate has a pair of apertures, each rotatably receiving a relatively large diameter pin. Each outer link has a pair of outer link plates rotatably mounted to the spaced pin members and a pair of outer keepers securely fit onto the ends of the pin members. The keepers in the outer link rows are washer shaped members located outside of the outer links.
Each inner link has a pair of inner link plates rotatably mounted to the pin members and a pair of inner keepers securely fit onto the pin members. The keepers in the inner link rows are located inside of the inner links and maintain a central section of the pin members in an exposed condition for engagement with a sprocket having a single row of teeth.
The chain of the present invention is also suitable for use with a variety of sprocket tooth forms, including sprockets with dual rows of teeth. In this instance, the inner keepers are eliminated and the inner links are located at the center of the pin members. The outer links and outer keepers are positioned inward from the pin ends as well, flanking the inner links, thereby leaving the ends of the pins exposed to engage with the dual rows of sprocket teeth. The inner and outer links wrap over the sprocket in the space between the rows of teeth.
In this second embodiment, randomization to achieve noise reduction is accomplished by providing pins having varied lengths between link rows. Varying the pin lengths between a first set of pin members having a first length and other pin members having different lengths and ordering the different pin lengths in a predetermined random pattern attempts to randomize or alter the pattern of contacts with the sprocket to result in generation of less noise than is produced by identical pins impacting the dual row sprocket.
Altering the profile of the sprocket teeth, as is known in the art is another technique expected to produce noise reduction with the chain assembly of the present invention.
In addition, causing one row of the dual sprocket to become slightly out of phase with respect to the other may also result in a reduction in generation of noise. In this instance, as the chain engages the sprocket, one end of each pin will engage a respective tooth before the other end engages a tooth on the other row of the sprocket.
The pins of the present invention preferably have a diameter near or equal to the diameter of a standard roller. By making the link plates thicker in the chain of the present invention as compared to the link plates of a conventional roller chain, the pins can have a relatively large diameter and the chain will possess the same or greater load capacity of a conventional roller or rollerless chain.
Since only one type of link plate is necessary for the chain of the present invention, variation between link plates is reduced. Thus, control of link lengths and aperture diameters is improved. Reduction of the number of parts necessary to produce the chain simplifies manufacturing, which reduces manufacturing costs and improves quality control.
For a further understanding of the present invention and the objects thereof, attention is directed to the drawings and the following brief description thereof, to the detailed description of the preferred embodiments of the invention and to the appended claims.